(a) Field
Apparatuses employed for the containment of plasmas by magnetic fields may utilize many varied configurations. Two well-known categories of these machines are the open-ended type such as the magnetic mirror and the toroidal type such as the tokamak and the stellarator. One advantage to the toroidal type is that a trapped charged particle must move laterally across magnetic field lines to escape confinement. Hereinafter, positive ions will be designated simply as "ions." Since the ions tend to remain in a spirial orbit about a given set of magnetic field lines, the continuity of the magnetic field lines inside the apparatus enhances containment.
An apparatus of the open-ended type has the disadvantage that the trapped charged particles may escape while traveling along the magnetic field lines which define their spiral orbits. The magnetic field lines do not close upon themselves inside the simple magnetic mirror. As a result, the simple magnetic mirror suffers large plasma losses through the mirror ends. The net positive potential of the confined plasma adds to the losses since ions are confined better than electrons in a simple magnetic mirror. One early mirror confinement apparatus is disclosed in Post, U.S. Pat. No. 3,170,841, filed on July 14, 1954. The physics of a simple magnetic mirror is discussed at length in the Post patent as well as in Samuel Glasstone and Ralph H. Loveberg, Chapter 9, "Magnetic Mirror Systems," Controlled Thermonuclear Reactions, D. Van Nostrand Co., Inc., Princeton, New Jersey (1960), p. 336 et seq and in David J. Rose and Melville Clark, Chapter 10, "Motion of Individual Charges," Plasmas and Controlled Fusion, John Wiley & Son, Inc., New York (1961) p. 198 et seq.
(B) Prior Art
The problem of end losses in magnetic mirrors has been addressed in a number of ways. One approach links several mirrors together to form roughly a toroidal configuration with magnetic field lines closed inside the apparatus. Particles which leak out of one magnetic mirror simply leak into an adjacent magnetic mirror. Post noted this in FIG. 25 of U.S. Pat. No. 3,170,841, supra. Other closed systems of linked magnetic mirrors include Dandl, U.S. Pat. No. 3,728,217. Each magnetic mirror segment is independent of the next, the total effect on the toroidally confined plasma being a stabilization due to the bumpy nature of the toroidal magnetic field. No mirror cell electrostatically plugs the ends of any adjacent mirror cells. The same may be said for other linked mirror systems such as the Christofilos, U.S. Pat. No. 3,668,067. In both Dandl and Christofilos, the linked magnetic mirrors are secondary to the stabilization and confinement of the plasma, which is by means other than by electrostatic plugs.
In linked three-cell systems, the earliest prior art appears in FIG. 22 of Post, U.S. Pat. No. 3,170,841. However, Post's three-cell system does not operate as three cells simultaneously. The end cells exist as thermonuclear reaction zones alternately and do not serve to electrostatically stopper the central cell.
A three-mirror system to change the potential at the linking magnetic mirrors is suggested by G. G. Kelley, 9 Plasma Physics 503 (1967). Since electrons travel more freely through the mirroring regions than ions, the mirroring regions have a net negative charge. Thus, ions which would have mirrored are drawn deeper into the mirroring region, and some are lost. To overcome this enhanced end loss, Kelley injected cold neutral species into the mirroring regions of the center mirror cell of a three mirror cell system. The cold neutral species ionize; thus, these mirroring regions substantially lose their negative potential. Kelley did not try to make the end mirror cells electrostatic end plugs to stop end losses in the center mirror cell. He addressed a problem of enhanced end losses without touching on the basic end-loss problem in an open-ended system.
The problem of end losses in an open-ended system has not been solved by the prior art. If the loss of plasma out the ends of a mirror cell can be substantially reduced, the mirror cell will occupy an enhanced position with respect to toroidal plasma containment apparatus. The mirror cell will lose less plasma and accordingly will lose less of the energy the plasma represents.